In drilling operations, the derrick is the structure designed to support and manipulate the drill string in and out of the well bore. The drill string is a series of drill pipe segments detachably connected together. Typically, the drill pipe segments are coupled together to form a pipe stand of a predetermined or standard length and the pipe stands are then coupled together to form the drill string.
A drill collar and a drill bit are attached to a drill end of the drill string. The drill collar is a heavier pipe having a larger diameter which fits around the drill pipe and places weight on the drill bit such that the downward force from the weight of the drill string, drill collar, and other drilling equipment on the drill bit assists in the drilling process. As the drill bit and drill string rotate and penetrate into the well bore, additional lengths of pipe stands may be connected to the coupling end of the drill string. Each pipe stand is typically thirty to forty five feet in length for larger drilling operations and between fifteen and twenty feet for smaller operations.
Because the drill bit has to be changed after a few days or even a few hours, depending on the hardness of the matter being drilled through, the drill string must be raised and lowered frequently. This involves withdrawing the drill string from the well bore by conventional hoisting means such as a winch mounted to the derrick, uncoupling the pipe stands of the drill string using a power wrench, and stacking the pipe stands in a conventional pipe storage or racking assembly such as a finger board assembly. In larger operations, the drill string can weigh several hundred tonnes and requires an extremely powerful motor housed in the derrick to withdraw the drill string from the well bore. Typically, electric or hydraulic pipe handling systems transport pipe stands between the well bore and the derrick to and the storage assembly. After replacing the bit, the pipe stands are removed from the storage assembly by the pipe handling system and transported back to the drill string where the pipe stands are re-coupled with the drill string and lowered back down the well bore to recommence drilling. Known as a “round trip”, this operation can take up to ten hours or more, depending on the depth of the well.
There are several devices and apparatus known in the art designed to improve the efficiency of the round trip operation. For example, U.S. Pat. No. 4,621,974 to Krueger, issued Nov. 11, 1986, provides an automated pipe equipment system for automatically removing pipe stands from and adding pipe stands to a drill string by using sensing means such as transducers to indicate to a programmable controller whether a pipe joint has been grasped by a racking arm. This system increases the efficiency of the round trip operation by reducing the manual labour typically required to facilitate various steps in the operation, such as ensuring that the racking arm has securely grasped the pipe stand. Furthermore, U.S. Pat. No. 4,117,941 to McCleskey Jr. et al., issued Oct. 3, 1978, provides a device which rapidly handles and vertically racks riser pipes and drill pipes in the drilling derrick. Manipulators effect the desired displacement of the pipes such that the lower ends of the pipes may rest on a set back platform on the drill floor and the upper ends of the pipes may be secured in a finger board. In addition, U.S. Pat. No. 4,013,178 to Brown et al., issued Mar. 22, 1977, provides a pipe racker wherein a manoeuvrable arm mounted on the derrick may grip the pipe joint anywhere along its length, lift the pipe, and move the pipe to another location without the need of a cable support. The vertical, horizontal and telescoping of the manoeuvrable arm provides the racker with three orthogonal degrees of freedom
While the prior art provides devices for handling pipe stands in a more efficient manner, they do not provide a solution to address the instability associated with manipulating and transporting pipe stands that may exceed thirty feet in length and several hundred tonnes in weight. For example, in the Krueger patent, a clamp engages only an upper portion of the pipe to effect vertical and rotational movement, leaving the mid-portion and lower portion of the pipe vulnerable to undesired swaying movement which may affect the racking rate. Furthermore, the repeated use of clamps and other similar securing means causes scarring of the pipe stands which eventually causes weakening and breakage of the pipe stands. Conventional securing means used in the art also fails to provide proper or adequate support of the weight of the pipe stand. Therefore, an unaddressed need exists in the industry to provide an apparatus for handling pipes in a stable and efficient manner to deal with deficiencies and inadequacies in the prior art.